In the field of the manufacture of products such as tortillas, efforts have been increasingly directed toward reducing costs and toward increasing the speed of production. Thus, the manufacture of wheat tortillas has evolved over the last few years into several different means and methods of production.
One such means is to die-cut the tortillas. In this means, tortilla dough is mixed in a 300-400 pounds horizontal mixer. The dough is transferred to the feed hopper of a single or double screw extruder which extrudes a 1" thick sheet of dough onto the conveyor belt of a rolling-cutting machine. In the latter, by rolling the dough in a direction which is sideways to the direction of travel of the belt ("cross-rolling"), and lengthwise ("sheeting"), the dough ribbon is gradually reduced to an endless sheet of dough about 30" wide. As the sheet is processed, a subtantial amount of dusting flour is used to prevent sticking of the sheet to the conveyors and the sheeter rolls. A rotating die cuts tortillas in the form of circular cut-outs. The cut-outs are then seperated from the remaining grid of dough, the tortillas exit the machine into an oven where they are cooked, and the grid is returned to the feed hopper of the extruder for reprocessing. Typically, such an apparatus produces 6" and 8" tortillas a the rate of about 1700 dozen per hour or about 1200 dozen per hour for 10" tortillas. This high production rate coupled with a low labor factor produces a low cost product. However, the product itself is not of the best quality because a large portion of the extruded and rolled sheet which forms the grid which, when reprocessed along with the large amount of dusting flour which it bears, inhibits re-mixing, tends to produce a layered sheet, renders the final product substantially inflexible after a few days, produces a product which cracks when bent into forms such as a burrito, and is "sandy" to the taste.
Another means of producing such products is by "hand stretching". Here dough balls are made in apparatus called a (dough) "divider-rounder" which apportions the dough and the forms each portion into a ball. The balls are "proofed" for about 5 minutes; i.e., the dough is allowed to relax after having been overworked in the ball maker. The balls are fed through a "double cross" roller mechanism which rolls the dough in two directions (at a right angle) down to the thickness of the final tortilla product. Since this rarely produces satisfactorily round products, they are stretched into roundness by hand on a table which is heated to stabilize them in shape. Typical installations range in output from 800 dozen per hour for 6" tortillas to 350 dozen per hour for 10" tortillas. The advantages of this method are that the dough is handled more gently and it is proofed prior to sheeting, and less sheeted dough is generated for re-cycling. The resulting product is more flexible and therefore more satisfactory for producing such products as burritos, although it still bears substantial amounts of dusting flour. The chief disadvantage is a very high labor cost, because virtually every piece produced must be hand formed.
Another process for forming tortillas is the so-called pressing method and apparatus. In this means, dough balls are formed in a divider-rounder, proofed in a proofer cabinet or an automatic proofer, and fed automatically or manually onto a conveyor which carries 6 to 12 dough balls at a time into position between the heated platens of a tortilla press. To attain a reasonable volume of production, a large amount of heat must be imparted to the tortillas by the platens to overcome their inherent tendency to resume their original shape, and thereby to thicken and shrink in size circumferentially. Therefore, the associated conveyor belt must possess a high heat tolerance. For those reasons, and to provide belts with sufficient properties of non-adherence, strength, flexability and durability, conveyor belts in common use consist of a woven fiberglass yarn base with a teflon covering. When a batch of dough balls has been properly positioned between the press platens, the conveyor is stopped and the press is closed on the dough balls for about one second, which squeezes the balls into round, "pancake" shaped tortillas that are then transferred into an oven for baking. Since the heating of the tortillas during pressing to stabilize them in shape and size also melts some of the shortening in the dough, dusting flour is not reguired and the result is a superior, better tasting product. However, having to start and stop the conveyor each time a new group of dough balls is presented by it to the press severely limits the output of such apparatus to the range of from about 350 to 500 dozen 6"-8" tortillas per hour.
These speed cycles limit production due to the time consumed while the belt is stopped. They also introduce other difficulties which prevent reaching desired production speeds and quality levels. The composition of the belt is dictated by the physical and thermal environment to which it is exposed, and the requirement that it be sufficiently non-adhering for the end product to be easily removed from it. One of its characteristics of acceptable materials is that they are inherently slick, particularly when the feature of non-adherence is adequately accommodated. This seriously limits the rate at which there can be acceleration and deceleration of the belt during each of its stop-start cycles, so that the volume of production is further seriously limited; otherwise the inertia of the dough during speed changes causes it to slip out of position, particularly if it is in the form of a ball. One approach to reducing incidence of this is to try to increase the ability of dough to adhere to the top surface of the belt by having operators position the balls on the belt and manually press down on each of them, but that expedient is expensive and time consuming. If such shifts occur, they may cause the finished tortillas to overlay each other, or to be totally outside or only partially within the press area. That can cause the tortillas which are pressed to become sufficiently out of round, irregularly or incompletely pressed, and/or of non-uniform thickness to render them not useful or acceptable commercially and therefore lost production. Those results also can occur when the opposition of the dough balls to the closure of the platens during the pressing operation is not substantially uniform throughout the opposing surfaces of the platens. That can happen when dough shifts or where there are voids in the pattern of dough units exposed to the press. The platens will then tend to come together out of parallal planar relationship to each other, causing uneven flattening within and among the tortillas in that batch. It may also introduce potentially damaging lateral moments of force on the piston rod of the hydraulic cylinder mechanism that is typically used to actuate the upper platen of the press in its upward and downward traverses. Although the possibility of these effects will be reduced substantially by the constant feed feature of the present invention, it is also desired to provide other means to avoid them totally and in any event. That is because even when inertial displacement of the dough balls which the present invention is designed to avoid does not take place, there still may be irregularities in the geometry of their placement. For example, the dough ball dispenser may fail to place a ball where one should have been positioned or, in a manual operation, an operator may miss placement of one or more balls.
In addition, such prior art processes and apparatus, particularly when there are voids in the distribution and/or mass of tortillas being cooked, may cause difficulties in controlling the amount of heat in the ovens in which they are subsequently cooked and the extent to which products passing through the oven are cooked, and may detract from the efficient use of fuel. The intermittant loading of the oven which results when successive batches of dough are introduced into the ovens causes variations in the amount of heat being extracted from the oven by the cooking process and in the temperature in the oven over any given span of time. This may cause some of the tortillas to be undercooked if they are placed in the oven immediately following a large mass of dough, or overcooked and even burned (particularly around the edges) if they are introduced into the oven after it has been unoccupied for a while. To avoid such temperature "ranging", the amount of fuel used in the oven may be varied, but this results in inefficient fuel utilization, as also does overheating.
Yet another problem with prior art apparatus of this type is that the belts used with them tend to become fouled with bits of dough and other debris. When exposed to the heating effects of the platens, such deposits can become carbonized to form hot spots where there is consequent rapid deterioration of the belt and sometimes burning of holes in it, ultimately rendering it unusable.
Thus, some of the major disadvantages of the prior art apparatus and methods in this field are low productivity per unit time, high manpower requirements, sanitary difficulties where the constituent dough is manually handled, poor product consistency, poor product quality, poor fuel efficiency, high scrap rates, and intermittent production and oven loading.
Accordingly, it is an object of this invention to provide means for the continuous automated production of objects made from dough that are stabilized in a pancake-like shape.
Another object of this invention is to provide means which will achieve the foregoing object with increased production speeds, reduced scrap, and improved energy efficiency.
Still another object of this invention is to provide means to achieve the foregoing objects with improved life of the constituent elements of the apparatus used.
Yet another object of this invention is to provide means to achieve the foregoing objects which may be integrated with other known per se means for producing products such as tortillas.